1. Field of the Invention
The present invention relates to an apparatus for manufacturing a unit of laminated ceramic green sheets. More specifically, the present invention relates to a technique for manufacturing a unit of laminated ceramic green sheets that may be incorporated in a laminated capacitor, or multilayer printed circuit board, by way of example.
2. Description of the Prior Art
Products incorporating ceramic green sheets include, for example, a laminated capacitor. When manufacturing a laminated capacitor, a laminated unit of ceramic green sheets is used. Methods of making such a laminated unit of ceramic green sheets, for example include the so-called "doctor blade" method, disclosed in Japanese Patent Publication No. 19975/1965, published on Sept. 6, 1965, and the screen printing method, disclosed in Japanese Patent Publication No. 12008/1984, published on Mar. 19, 1984.
In the conventional doctor blade method, the ceramic green sheets on which conductive paste is printed are formed one by one, and the sheets are then laminated together to form a laminated unit of ceramic green sheets. In this method, the ceramic green sheets have to be laminated to each other one by one to form the laminated unit, and accordingly, this method is complicated and is not well-suited to mass production techniques.
In the screen printing method, a process is repeated wherein a dielectric ceramic slurry is printed with a silk screen to form a ceramic green sheet, and on such sheet a conductive paste is printed to form inner electrodes. Although this screen printing method is more amenable to mass production than the doctor blade method, the screen printing method suffers from the following problems.
In particular, since a screen is employed in this method, not only is the imprint of the screen mesh left intact in the resulting green sheet as a concave-convex pattern, but also the thickness of the resulting ceramic green sheets is difficult to control, making it nearly impracticable to obtain the required thickness.
Moreover, when ceramic green sheets of nonuniform thickness with electrodes thereon are laminated together to form a unit, such lack of uniform thickness of the ceramic green sheets is likely to lead to delamination of the unit. To prevent such an occurrence of delamination, the surface of the ceramic green sheet must be flat. For this reason, an extra procedure is required wherein the ceramic slurry is printed to a thickness equivalent to the thickness of an inner electrode, on any portions of an underlying ceramic green sheet that are not covered by the corresponding inner electrode. Also, when the position of the ceramic slurry printed in the additional process is shifted, difficulty in producing a terrace, or the like, further takes place.
In addition, another problem of the screen printing method is such that if foreign matter is trapped in the screen mesh, the location of such foreign matter results in a pinhole in the resulting sheet. Moreover, if printing with such a soiled screen is made many times, each resulting ceramic green sheet has a similarly located pinhole and, as a consequence, the inner electrodes become short circuited to one another when such ceramic green sheets are incorporated into a product such as a laminated capacitor.